A cyclist traversed half the distance of a linear track with a velocity 10 m/s. The remaining part of the track was covered with a velocity
$\overline{{\mathrm{v}}_1}$for half the time and a velocity $\overline{{\mathrm{v}}_2}$ for the other half of the time. If $\overline{{\mathrm{v}}_1} + \overline{{\mathrm{v}}_2} = 20 \mathrm{m}/\mathrm{s}$, then the average velocity of the cyclist during the completion of the journey through the track is